For more plots see my COVID-19 directory.
Growth rate over a seven day window in Brazil on 2020-07-08 is 1.024. Hence the numbers double every 28.9 days.
This plot has a logarithmic y-axis to illustrate the exponential growth.
The cases[t] − cases[t−28d] is the number of cumulated cases minus the number of cumulated cases four weeks ago, which should serve as the very crudest estimate of the number of persons being infected at that time.